1. Field of the Invention
The present invention relates to a tensioner including a tensioner body having a cylindrical plunger housing hole that is open at one end, a cylindrical plunger slidably inserted into the plunger housing hole, and bias means for biasing the plunger in a protruding direction, and a rocking lever having a guide surface that comes into sliding contact with a traveling endless transmission member, a boss portion supported so as to be able to rock, and a pressing surface provided on a side of the rocking lever opposite to the guide surface.
2. Description of the Related Art
A tensioner and a swinging lever are conventionally commonly used to properly maintain the tension of an endless transmission member such as a traveling chain. For example, a chain guide mechanism for a timing system is well known in which a traveling guide shoe is used to slidably guide a transmission chain such as a roller chain endlessly passed between sprockets provided on a crank shaft and a cam shaft in an engine room and in which a tensioner is used to bias a rocking lever with the traveling guide shoe in order to properly maintain tension.
In the timing system for the engine, for example, as depicted in FIG. 7, a timing chain CH is endlessly passed between a driving sprocket S1 attached to a crank shaft in the engine room and a pair of driven sprockets S2 and S3 attached to a cam shaft in the engine room. The timing chain CH is guided by a rocking lever 550 and a fixed chain guide G2.
The fixed chain guide G2 is fixed in the engine room using two attachment shafts B1 and B2. The rocking lever 550 is attached to the inside of the engine room so as to be able to rock in a passage plane for the timing chain CH.
A chain tensioner 500 presses the rocking lever 550 to properly maintain the tension of the timing chain CH while suppressing vibration.
The well-known tensioner 500 used to press the rocking lever 550 includes a tensioner body 510 having a cylindrical plunger housing hole 511 that is open at one end, a cylindrical plunger 520 slidably inserted into the plunger housing hole 511, and bias means including a coil spring 530 that biases the plunger 520 in a protruding direction through the plunger housing hole 511, for example, as schematically depicted in FIG. 8.
Oil is fed into the plunger housing hole 511 to bias the plunger 520 in the protruding direction. As the plunger 520 makes reciprocating motion, the oil flows through a small gap between the plunger 520 and the plunger housing hole 511. The resultant channel resistance produces a damping effect that dampens the reciprocating motion of the plunger 520.
As depicted in FIG. 7, the well-known rocking lever 550 pressed against the tensioner 500 has a guide surface 551 that comes into sliding contact with the traveling timing chain CH, a boss portion 552 supported by an attachment shaft B0 so as to be able to rock, and a pressing surface 553 provided on a side of the rocking lever opposite to the guide surface 551.
In such a timing system, when the tensioner is assembled or removed for maintenance, the plunger needs to be fixed at a position to which the plunger is pushed back, so as not to protrude from the tensioner body.
Thus, a technique is known in which a body pin hole (pin through-hole 11b) is formed in a tensioner body (tensioner main body 11) and in which a stopper pin (S) is inserted through the body pin hole and locked in a ring-like pin locking groove (12b) formed in a plunger (12) to fix the plunger, for example, as depicted in Japanese Patent Application Laid-open No. 2001-153194.
However, in the technique described in Japanese Patent Application Laid-open No. 2001-153194, since the body pin hole (pin through-hole 11b) is formed in the tensioner body (tensioner main body 11), the ring-like pin locking groove (12b) needs to be formed at a certain distance from a tip of the plunger (12). Thus, the volume of a space provided inside the plunger (12) is limited.
Furthermore, the stopper pin (S) is locked only along a length equal to the depth of the ring-like pin locking groove (12b) and thus a heavy load is placed on the stopper pin (S). Consequently, the stopper pin may be damaged or fall out, leading to abrupt protrusion of the plunger (12).
Meanwhile, a rocking lever is known in which, to position the plunger in a width direction of a pressing surface when a tip portion of the plunger comes into abutting contact with the pressing surface, lips protruding from the pressing surface are provided on opposite sides of the pressing surface in the width direction.
In particular, when an oil chamber is formed inside the plunger and oil is fed into the plunger through a side surface thereof, the plunger needs to be prevented from rotating so as to avoid changing the position of an oil feeding hole of the plunger in a circumferential direction. A technique is well known in which the tensioner itself has no locking mechanism and in which two parallel tip side surfaces are provided at a protruding end of the plunger such that the lips of the rocking lever are used for locking.
Such lips come into abutting contact with or come very close to the plunger protruding side of the tensioner body when the plunger lies at a position where the plunger is pushed back.
Thus, when the rocking lever with the lips is used, the body pin hole in the tensioner body needs to be located further away from the tip of the plunger, disadvantageously further limiting the volume of the space provided inside the plunger.